This is a proposal to continue present studies aimed at establishing a link between sudden infant death syndrome (SIDS, also known as crib death) and malfunctioning autonomic reflexes. Study A is to characterize the development of autonomic function of normal term and premature infants during the first year of life. The characterization is based on by-weekly determinations of naturally occurring variations in respiratory and heart rate patterns during sleep. Since susceptibility to SIDS is greatest during the second to fourth months of life, pronounced changes in cardio-pulmonary control during this time interval will be sought. The first year of the current studies has disclosed a number of features of respiration and heart rate variation that undergo changes during the first year of life. Further studies are needed to quantitate these changes during active sleep, and to test a sufficient number of infants to allow statistical analysis of the data. Study B is to characterize autonomic function in tose high-risk infants who are hospitalized with apneic spells of unknown etiology. These infants are considered "near-miss" SIDS cases. The measures of cardio-pulmonary control for high-risk and normal infants will be compared in an attempt to determine if susceptibility to SIDS can be demonstrated. The first year of the study showed that pronounced and/or prolonged bradycardia accompanies apnea in high-risk infants. Continuing studies will attempt to determine if it is secondary to hypoxia or it is due to massive parasympathetic discharge. Preliminary indications that urinary catecholamine levels may correlate with physiological assessment of autonomic function will be also further investigated.